Studies have been designed to ascertain the mechanism by which lymphoma develops in immunodeficient humans, utilizing the athymic mouse as a model system. Lymphomas are induced in this genetically defective animal when pinworms or human xenografts are present. There is a possibility that a viral glycoprotein (gp70) is involved in the induction of this malignancy. The properties, structure, function, and regulation of the synthesis of this protein will be investigated. Studies will be carried out on factors from human tumors which may induce sarcomas in the athymic mice. These factors will be characterized and compared to other factors known to have similar functions. Extracted DNAs from a select group out of fifty-five human tumor xenografts carried in the athymic mice will be examined for their capacity to transfect normal cells into the malignant state. The nature and mechanism of activation of the involved genes will be investigated. The various transformants also will be compared for metabolic alterations. Phosphatases are present in the plasma membranes of the human astrocytoma; these enzymes cleave protein-bound phosphoserine and phosphotyrosine, and there appears to be distinct enzymes acting on the two phospho-amino acids. Preliminary results indicated that the phosphatases might be under regulation by phosphorylation. The various kinases and phosphatase will be purified from the plasma membrane and their characteristics determined. The significance of phosphorylation-dephosphorylation phenomenon in the plasma membrane will be investigated. (S)